1. Field of the Invention
The present invention relates to the recovery of elemental sulfur from a stream of hydrogen sulfide containing gas and, more particularly, the present invention uses recycle gas to moderate the temperature within a Claus reaction furnace.
2. Setting of the Invention
It is well known to remove elemental sulfur from a stream of hydrogen sulfide containing gas using a Claus reaction furnace to combust a portion of the hydrogen sulfide to sulfur dioxide which is then thermally or catalytically reacted to product elemental sulfur. Occasionally, an existing sulfur recovery plant is modified to increase the capacity of the Claus reaction furnace to handle hydrogen sulfide by adding an oxygen-enriched gas to the air feed. U.S. Pat. No. 3,681,024 describes a process that uses oxygen enrichment wherein a portion of the effluent gas from the downstream portion of the plant is recycled to the Claus reaction furnace to control the temperature therein. U.S. Pat. No. 4,552,747 describes another process that uses oxygen enrichment wherein a portion of the effluent from a sulfur condenser downstream of the Claus reaction furnace is recycled to control the temperature therein.
The inventors hereof have found that in some instances an unacceptably large pressure drop across the unit can occur, especially across the first condenser unit. Also, the effluent flow rate and temperature from the condenser used in recycling can be higher than desired, necessitating the use of more expensive valves and a larger capacity blower.
Other problems associated with the process of U.S. Pat. No. 4,552,747 is that if the condenser effluent temperature is lowered to facilitate recycling, then overall sulfur recovery can be reduced when hot gas bypass or acid gas fired in-line burners are used to reheat the feed to the subsequent reactor because a greater portion of the rich process gas is introduced into the reactor. If a non-fired indirect heater is used, instead of hot gas bypass or acid gas fired in line burner, then no heat source adequate for heating the effluent to operating temperature of the first reactor is present.
If, on the other hand, the temperature of the first condenser's effluent is not reduced, then a larger blower for recycling will be required, more expensive materials will be required, and maintenance requirements will be greater.
There exists a need for a method of recovering sulfur which utilizes oxygen-enriched air in the Claus reaction furnace and which utilizes recycle gas for temperature moderation which reduces or eliminates the above-described disadvantages of the prior art processes.